THE CORE OF THE MAMMALIAN CENTRIOLE CONTAINS GAMMA-TUBULIN

Background: The microtubule network, upon which transport occurs in hi gher cells, is formed by the polymerization of alpha and beta tubulin. The third major tubulin isoform, gamma tubulin, is believed to serve a role in organizing this network by nucleating microtubule growth on microtubule-organizing centers, such as the centrosome. Research in vi tro has shown that gamma tubulin muse be restored to stripped centriol es to regenerate the centrosomal functions of duplication and microtub ule nucleation. Results: We have re-examined the localization of gamma tubulin in isolated and in situ mammalian centrosomes using a novel i mmunocytochemical technique that preserves antigenicity and morphology while allowing increased accessibility. As expected, or tubulin was l ocalized in cytoplasmic and centriolar barrel microtubules and in the associated pericentriolar material. Foci of gamma tubulin were observe d at the periphery of the organized pericentriolar material, as report ed previously, often near the termini of microtubules. A further and m ajor location of gamma tubulin was a structure within the proximal end of the centriolar barrel. The distributions were complementary, in th at a tubulin was excluded from the core of the centriole, and gamma tu bulin was excluded from the microtubule barrel. Conclusions: We have s hown that gamma tubulin is localized both in the pericentriolar materi al and in the core of the mammalian centriole. This result suggests th at gamma tubulin has a role in the centriolar duplication process, per haps as a template for growth of the centriolar microtubules, in addit ion to its established role in the nucleation of astral microtubules.